An optically addressed liquid crystal light valve is used widely in the field of optical information processing, optical computing, etc. A first conventional optically addressed liquid crystal light valve which is well known is one manufactured by Hughes Aircraft Company of the U.S. In the optically addressed liquid crystal light valve, nematic liquid crystal is sandwiched between a glass substrate and an opposite substrate. The glass substrate is provided with a plurality of photoconductors of CdS and dielectric mirrors, and the opposite substrate is provided with a transparent electrode.
On the other hand, an optical arithmetic process carried out by an optical logic device using such an optically addressed liquid crystal light valve has been disclosed in an article titled "DIGITAL OPTICAL COMPUTING" on pages 758 to 779 of PROCEEDING OF THE IEEE, Vol. 72, No. 7July 1984. In the optical arithmetic process, AND and OR arithmetic processes, and so on, are carried out between two input images by using optical threshold characteristic of a reading light relative to a writing light in the optically addressed liquid crystal light valve.
A second conventional optically addressed liquid crystal light valve is described in the previous text 30a-ZD-8 of 50th science lecture of APPLIED PHYSICS SOCIETY. In the optically addressed liquid crystal light valve, amorphous silicon and ferroelectric liquid crystal are used instead of CdS and nematic liquid crystal, and optical arithmetic processes using the light valve are carried out. The light valve has an advantage of high speed operation, because ferroelectric liquid crystal used therein has higher speed of response by two or three figures compared with nematic liquid crystal.
According to the conventional optically addressed liquid crystal light valve, however, there are disadvantages as explained below. In the first conventional optically addressed liquid crystal light valve, the speed of response which is determined by the speed of response of CdS and nematic liquid crystal is as low as up to 30 ms. Such a low speed of response of the light valve may become obstacles to higher speed operation of optical arithmetic processes. Further, the optical contrast thereof is not high because the change of voltage applied across the liquid crystal is low between binary states. The voltage applied across the liquid crystal is determined by a capacitance dividing ratio of the photoconductor and the dielectric mirror composing the light valve. Capacitance of the dielectric mirror will not change even if capacitance of the photoconductor changes, so that the voltage applied to the liquid crystal will not change largely. Such a low contrast thereof may not badly affect optical arithmetic processes if the light valve is used discretely in the processes, because outputs of the optical arithmetic processes are supplied as binary data of states of bright and dark. However, it is difficult to supply outputs correctly from the previous stage of the light valve to inputs of the next stage thereof in case that a plurality of light valves are connected serially to form a multi-stage structure if the contrast is not sufficiently high. Additionally, it is difficult to carry out different arithmetic processes such as AND, OR or exclusive OR processes simultaneously in one light valve, because the arithmetic processes are carried out by using optical threshold characteristic of a reading light relative to a writing light in the light valve. The whole surface of the light valve is uniform and only one of either arithmetic process can be carried out, so that it is difficult to carry out two or more kinds of arithmetic processes simultaneously.
In the second conventional optically addressed liquid crystral light valve, the speed of response is improved as compared with that of the first conventional optically addressed liquid crystal light valve, however, the same disadvantages of the low contrast and single-arithmetic-process ability as in the first conventional optically addressed liquid crystal remain.